Sealed open chamber breech mechanism



May 27, 1969 D. DARDICK SEALED OPEN CHAMBER BREECH MECHANISM ors SheetFiled Sept. 1, 1967 8 mo 4% I l 2 O 8 3| m L E 9 Fig.2

David Dordick ATTORNEY y 7, 1969 D. DARDICK 3,446,113

SEALED OPEN CHAMBER BREECH MECHANISM Filed Sept. 1, 1967 Sheet 2 of 3Fig,4

David Dordick mvsmon ATTORNEY May 27, 1969 o. DARDICK SEALED OPENCHAMBER BREECH MECHANISM Sheet 3 of 3 Filed Sept. 1, 1967 ATTORNEYUnited States Patent 3,446,113 SEALED OPEN CHAMBER BREECH MECHANISMDavid Dardick, Palos Verdes Peninsula, Califl, asslgnor to TRW Inc.,Redondo Beach, Calif., a corporation of Ohio Filed Sept. 1, 1967, Ser.No. 671,910 Int. Cl. F41f 11/04 U.S. CI. 8926 25 Claims ABSTRACT OF THEDISCLOSURE BACKGROUND OF THE INVENTION Field of the invention Thisinvention relates generally to so-called open chamber breech mechanisms.More particularly, the invention relates to a novel sealed open chamberbreech mechanism for firing caseless ammunition.

As will appear from the description, the open chamber breech mechanismof the invention is capable of application in both weapons andnon-weapon propellant gas actuated devices. In this regard, attention isdirected to the fact that the term ammunition is employed in thisdisclosure to encompass both projectile-type ammunition having both aprojectile and a propellant and projectileless ammunition having apropellant only. For convenience, the invention will be disclosed inconnection with its application to weapons, specifically guns.

Prior art Conventional guns for firing cased ammunition utilize a closedchamber breech mechanism having a four-step firing cycle involvingpositioning of each round in registry with the firing chamber, axialinsertion or ramming of the round into the chamber, axial extraction ofthe spent case from the chamber, and final ejection of the case. Thesefour basic steps are required regardless of the type of gun and areaccomplished partly by hand in some guns, such as a revolver, andautomatically in other guns, such as belt or magazine fed automaticweapons. These conventional closed chamber breech mechanisms and theirfour-step firing cycle are characterized by numerous disadvantages whichare well-known to those skilled in the art and thus need not beexplained in detail. Suflice it to say that one possible technique ofavoiding some of these disadvantages involves the use of caselessammunition. Caseless ammunition, for example, offers the followingbenefits. The necessity of extracting and disposing of hot metalliccartridge cases from the gun chamber after firing is eliminated. Thechamber is automatically emptied during firing. Caseless ammunitioncontains a greater mass of propellant than does cased ammunition of thesame overall size. Finally, caseless ammunition offers certain logisticadvantages including weight and cost reduction and weapon designsimplification. However, the use of caseless ammunition in conventionalautomatic weapons presents the following five major problems which stillawait satisfactory solution. First, a gas seal at all interfaces of thebreech closure, such as the junction between the breech block and barrelchamber as well as around the firing pin, is essential to satisfactoryutilization of caseless ammunition but is extremely difiicult to achievein an automatic closed chamber mechanism. Secondly, a chambered caselessround is extremely difficult to extract from a closed chamber breechmechanism in the event of a misfire or jamming. In this regard, forexample, it is significant to note that it is impossible to form an extractor lip on the base of the combustible case, or caseless round,which is strong enough to withstand extraction forces on the round.Third, there is a tendency for debulleting, i.e., separation of theprojectile from its propellant, to occur when a caseless round is rammedforwardly at high velocity into a gun chamber. Moreover, if misfireoccurs after debulleting, the projectile may remain in the gun bore whenthe propellant is extracted. Fourth, an unfired caseless round in a hotgun chamber is prone to cook 01f. The possibility of such cook offoccurring while extracting an unfired round presents a serious safetyhazard to the gun crew and equipment. Finally, the caseless roundscommonly employed in the existing closed chamber breech mechanisms arenot designed to withstand the forces and rough handling which arenormally encountered in conventional automatic gun operating cycles dueto stripping ofi' a belt link, ramming the round into the chamber, etc.

A relatively recent development in the gun art which avoids most if notall of the disadvantages of closed chamber breech mechanisms and theirfour-step firing cycle is the so-called open chamber breech mechanism.'Such an open chamber breech mechanism has a simple two-step firingcycle involving initial lateral infeed movement of each round intofiring position and final lateral ejection of the spent casing.Representative of the prior art relating to open chamber breechmechanisms are the following patents: No. 2,983,223, No. 2,831,401, No.2,847,784, No. 2,865,126, No. 3,041,939, and No. 3,046,890.

The existing open chamber breech mechanisms, while vastly superior toclosed chamber breech mechanisms for reasons Well-known to those skilledin the art and pointed out in the above patents, are characterized bythe deficiency that they are limited to use with cased ammunition andare thus unable to take advantage of the abovenoted benefits of caselessammunition. This results from the fact that the existing open chamberbreech mechanisms are devoid of obturator means for sealing the leakageinterfaces of the mechanisms against propellant gas leakage duringfiring.

SUMMARY OF THE INVENTION The present invention provides an open chamberbreech mechanism equipped with novel obturator means for sealing theinterfacial leakage spaces between the breech frame and the open chambercarrier or cylinder to permit firing of caseless ammunition withoutpropellant gas leakage from the firing chamber. According to a preferredfeature of the invention, the obturator means are actuated or urged toscaling position by the propellant gas pressure in the open chamberbeing fired. The obturator means may be carried by either or both thebreech frame and the open chamber carrier or cylinder of the breechmechanism. A refinement of the invention resides in a unique mounting ofthe breech cylinder, whereby effective interfacial sealing isaccomplished in such a way as to minimize the frictional resistance torotation of the cylinder to and from firing position.

At this point, attention is again directed to the fact that while theinvention will be disclosed in connection with its application to aweapon or gun, the sealed open chamber breech mechanism of the inventionmay 'be utilized to advantage in a variety of other non-weaponapplications.

BRIEF DESCRIPTION OF THE DRAWINGS In the drawings: FIG. 1 is alongitudinal section through a sealed open chamber breech mechanismaccording to the invention illustrating a round of the present caselessammunition in firing position within an open firing chamber of themechanism;

FIG. 2 is a transverse section through the breech mechanism taken online 22 in FIG. 1;

FIG. 3 is an enlarged, exploded perspective view of an open chambercarrier or cylinder and obturator means embodied in the breechmechanism;

FIG. 4 is a fragmentary longitudinal section through a modified, sealedopen chamber breech mechanism according to the invention for use in arecoilless weapon;

FIG. 5 is a longitudinal section through a further modified sealed, openchamber breech mechanism according to the invention for use withconventional caseless ammunition;

FIG. 6 is a transverse section through the modified breech mechanismtaken on line 6-6 in FIG. 5;

FIG. 7 is a longitudinal section through a sealed, open chamber breechmechanism according to the invention embodying modified obturator meansfor sealing the interfacial leakage spaces of the breech mechanism;

FIG. 8 is a section taken on line 88 in FIG. 7;

FIG. 9 is an enlargement of the area enclosed by the circular arrow 9 inFIG. 8; and

FIG. 10 is an enlarged fragmentary section through a sealed, openchamber breech mechanism according to the invention embodying furthermodified obturator means.

DESCRIPTION OF THE PREFERRED EMBODIMENTS In general terms, the inventionprovides a sealed, open chamber breech mechanism, represented in FIGS. 1through 3 of the attached drawings by the breech mechanism 10, forfiring caseless ammunition 12 according to the invention. The breechmechanism includes a hollow breech frame member 14, or breech frame asit will be hereinafter referred to, having a cylinder recess 16.Positioned within this recess is an open chamber carrier member 18. Thiscarrier member functions as, and in this instance has the general shapeof a cylinder. For this reason, the carrier member will be hereinafterreferred to in most places as a cylinder member, or simply a cylinder.The open chamber carrier or cylinder 18 is supported by means 20 on thebreech frame for rotation on an axis 22.

Formed in the circumference of the cylinder is a firing chamber 24. Thischamber opens through the circumference of the cylinder, laterally ofits axis 22, whereby the chamber has an open side. Cylinder 18 isrotatable between an ammunition infeed position wherein firing chamber24 registers with an ammunition infeed opening 26 in the breech framefor receiving through the opening a caseless ammunition round 12, and afiring position (FIGS. 1 and 2), wherein the breech frame closes theopen side of the firing chamber to condition the breech mechanism forfiring the caseless round. Firing of this round in the closed chamber 24generates a high pressure propellant gas in the chamber. Extendingthrough the breech frame 14 is a bore 28 which communicates with firingchamber 24 when the cylinder 18 occupies its firing position of FIGS. 1and 2 and through which the propellant gas exhausts from the chamberduring firing of the round 12 in the chamber. In this instance, the bore28 is a gun bore through which a projectile 30 embodied in the caselessround is driven by the propellant gas.

The open chamber breech mechanism 10 has a number of interfacial regionsor interfaces between the breech frame 14 and the cylinder 18 whichdefine potential propellant gas leakage spaces communicating with thefiring chamber 24 when the cylinder occupies its firing position. Theleakage interfaces of the illustrated breech mechanism 10, for example,include upper longitudinal and lateral interfaces 32, 34 surrounding theopen side of the firing chamber, a front interface 36 surrounding thebore 28, and a rear interface 38 surrounding a firing mechanism 40 forfiring the caseless round 12 in the firing chamber. An important aspectof the present invention is concerned with sealing these several leakageinterfaces against propellant gas leakage during firing of the caselessround 12 in the firing chamber. According to this aspect, the inventionprovides obturator means 42 for effecting the requisite sealingfunction. As will appear from the ensuing description, the illustratedobturator means comprise pressure responsive sealing elements which areurged to sealing position by the pressure of the propellant gasgenerated during firing. When thus urged to sealing position, thesealing elements effectively seal the several leakage interfaces 32, 34,36, and 38 of the breech mechanism against propellant gas leakage,whereby virtually the entire volume of propellant gas generated duringfiring is expelled through the bore 28. As noted earlier, and as willappear from the ensuing description, the obturator means may be carriedentirely by the breech frame 14, entirely by the cylinder 18, or partlyby the frame and partly by the cylinder.

Briefly, in operation of the illustrated open chamber breech mechanism10, the cylinder 18 is rotated to its ammunition infeed position,wherein the firing chamber 24 registers with the infeed opening 26 inthe breech frame 14. A caseless round 12 is then moved laterally intothe chamber, after which the cylinder is rotated to its firing positionof FIGS. 1 and 2. The firing mechanism 40 is then actuated to fire theround. In this instance, the resulting propellant gas pressure isutilized to drive the projectile 30 through the gun bore 28. It will berecalled, however, that an open chamber breech mechanism according tothe invention may be utilized for other purposes. During firing, theobturator means 42 effectively seals the leakage interfaces 32, 34, 36,and 38 to achieve maximum useable gas pressure. After firing, thecylinder 18 is again rotated to its infeed position to receive anothercaseless round 12.

Referring now in greater detail to the sealed, open chamber breechmechanism 10 of the invention which has been selected for illustrationin FIGS. 1 through 3, the breech frame 14 has a flat rectangular shapeand the cylinder recess 16 is defined by a generally rectangular openingin the frame which opens laterally through opposite sides of the frame.One side of this opening, i.e., the left hand side of FIG. 2, definesthe ammunition infeed opening 26 of the breech frame. Threaded in andextending forwardly fro-m the breech frame 14 is a barrel 44 whichcontains the gun bore 28. The axis of the barrel parallels the rotationaxis 22 of the open chamber carrier or cylinder 18.

Cylinder 18 has a generally cylindrical body 46. Extending axially fromthe front and rear ends of the cylinder body 46 are front and rearjournal formations 48 and 49, respectively. As shown best in FIG. 3,each journal formation has a bearing surface 50 which is cylindricallycurved about the rotation axis 22 of the cylinder and has acircumferential extent slightly in excess of Extending radially from theends of each bearing surface 50 to the circumference of the cylinderbody 46 are radial surfaces 52. Extending circumferentially between theouter ends of the radial surfaces 52 on the front journal formation 48is a conically tapered surface 54, the radially inner edge of which islocated radially inward of the circumference of the cylinder body 46.The rear journal formation 49 has a cylindrically curved surface 56extending between the outer ends of its radial surfaces 52, flush withthe circumference of the cylinder body.

The firing chamber 24 of the illustrated breech mechanism is elongatedin the longitudinal direction of the cylinder 18 and has its centralaxis located in a plane containing the central axis of the cylindricalbody 46 and passing midway between the radial faces 52 of the cylinderjournal formations 48, 49. The front end of the firing chamber is closedby a front end wall 58. Extending through this wall, on the central axisof the firing chamber, is a bore 60 which registers with the gun bore 28when the cylinder 18 occupies its firing position. Cylinder bore 60 andgun bore 28 have the same diameter which is somewhat less than the majortransverse dimension of the firing chamber 24. The rear end of thechamber is closed by an end wall 62. The illustrated chamber 24 has agenerally triangular round shape in transverse cross-section which isidentical to the cross-sectional shape of the firing chambers in theopen chamber breech mechanisms disclosed in the aforementioned prior artpatents. This chamber shape has certain advantages in the present breechmechanism which will be explained presently. The two side walls of thechamber are cylindrically curved to a radius of the cylinder 18.

The supporting means 20 for the breech cylinder 18 comprisecylindrically curved bearing surfaces 64 on the breech frame 14 at thefront and rear ends of the cylinder. The cylinder is installed in thebreech chamber in such a way that the cylindrical bearing surfaces 50 ofits journal formations 48, 49 rest slidable on the frame bearingsurfaces 64 and these surfaces support the cylinder for rotation on itsaxis 22. In the particular breech mechanism illustrated, the cylinder 18is movable with an oscillatory motion between its ammunition infeed andfiring positions. The radial surfaces 52 on the cylinder serve as stopshoulders which are engageable with the breech frame 14 to limitrotation of the cylinder. In this regard, it will be observed that thecylinder could conceivably rotate in either direction from its firingposition of FIG. 2 to infeed position. According to a preferred featureof the invention, however, the rotation axis 22 of the cylinder isdisplaced slightly from the central axis 66 of the cylinder body 46 tominimize the frictional resistance to rotation of the cylinder to andfrom its firing position, as hereinafter explained. In this case, thecylinder 18 may be rotated only in one direction from firing position toinfeed position. The cylinder of the illustrated breech mechanism, forexample, is rotatable in a counterclockwise direction, as viewed in FIG.2, from its firing position to its infeed position and in the clockwisedirection from its infeed position to its firing position. As alreadynoted and illustrated in the drawings, the rotation axis 22 of thecylinder 18 parallels the axis of the gun bore 28 so that rotation ofthe cylinder to its firing position locates the firing chamber 24 incoaxial alignment with the gun bore.

It will be recalled that an important aspect of the invention isconcerned with the obturator means 42 for sealing the leakage interfaces32, 34, 36, and 38 of the breech mechanism when the cylinder 18 occupiesits firing position. To this end, the obturator means comprise an upperobturator 68 in the form of a generally flat rectangular bar of metal orplastic which is positioned between the upper side of the cylinder 18and the firing strap 70 of the breech frame 14 and is fixed to thestrap.

Obturator 68 is intended to seal the upper longitudinal and lateralleakage interfaces 32, 34. To this end, the obturator is provided withlongitudinal sealing means 78 for sealing the longitudinal interfaces 32and front and rear lateral sealing means 80, 82 for sealing the lateralinterfaces 34. These sealing means are constructed and arranged to beurged, by propellant gas pressure, into sealing relation withcorresponding sealing surfaces on the cylinder 18. The sealing surfacesfor the longitudinal sealing means 78 of the obturator, for example, arefurnished by the circumferential surface portions 84 of the cylinder 18which bound the longitudinal sides of the cylinder firing chamber 24.The sealing surface for the front obturator sealing means 80 isfurnished by the conical surface 54 on the front journal formation 48 ofthe cylinder. Finally, the sealing surface for the rear obturatorsealing means 82 is furnished by the cylindrical surface 56 on the rearcylinder journal formation 49.

The pressure responsive sealing action of the obturator 68 may beaccomplished in various ways. The illustrated obturator, for example,has a generally hollow configuration defining an internal cavity 86Within the obturator which opens toward the cylinder 18 and is boundedby side wall members 88 on the obturator. The obturator sealing means78, comprise inwardly directed sealing elements or flanges on theobturator wall members 88 having sealing surfaces disposed inconfronting relation to and curved to conform with the cylinder sealingsurfaces 54, 56, 84 respectively. Thus, the longitudinal obturatorsealing flanges 78 have cylindrically curved sealing surfaces disposedfor sealing engagement with the cylinder sealing surfaces 8 4. The frontobturator sealing flange 80 has a conically tapered sealing surface forengagement with the cylinder sealing surface 5 4. Finally, the rearobturator sealing flange 82 has a cylindrically curved sealing surfacefor engagement with the cylinder sealing surface 56. The severalobturator sealing flanges 78, 80, 82 are so dimensioned that thepressure of the propellant gas which enters the obturator cavity 86 fromthe cylinder firing chamber 24 during firing of a caseless round 12 inthe chamber and thereby acts on the inner pressure faces of the flanges,urges or deflects the flanges toward and into sealing engagement withthe respective cylinder sealing faces. It is now evident, therefore,that the obturator 68 is effective to seal the open side of the cylinderchamber 24 during firing.

As noted earlier, the obturator means 42 are also effective to seal thefront leakage interface 36 of the illustrated breech mechanism. To thisend, the obturator means comprise in internal circumferential obturatorgroove 92 in the wall of the front cylinder bore 60. This groove definesan annular sealing element or flange 94 about the front end of thecylinder bore. According to the present invention, the cylinder sealingflange 94, like the sealing flanges on the obturator 68, is dimensionedto be urged into sealing relation or contact with a confront sealingsurface 96 on the breech frame 14 surrounding the gun bore 28 andfurnished by the rear end face of the gun barrel 44. Thus, the frontsealing flange 94 is effective to seal the breech mechanism against gasleakage through the interface 36 between the confronting surfaces of thebarrel and cylinder 18.

There remains for consideration only sealing of the rear leakageinterface 38 created by the firing mechanism 40. In this regard, it willbe observed that the illustrated firing t mechanism comprises a firingpin 98 which extends slidably through a bore in the rear end wall 62 ofthe cylinder firing chamber 24 for contact with a primer 100 containedwithin the rear end of the caseless round 12. Fixed to the rear end ofthe firing pin 98 is a sealing flange 102 which is contained Within achamber 104 in the rear end wall 62. A spring 106 acting between thefront end of the latter chamber and the firing pin sealing flange urgesthe firing pin 98 to its retracted position of FIG. 1, wherein theforward end of the pin is retracted from the firing chamber 24.Extending through the rear end of the breech frame 14 and the rearfiring chamber wall 62 is a bore 108 which is adapted to receive ahammer pin 109 for driving the firing pin 98 inwardly against theigniter 100 to fire the caseless round 12 in the chamber. The combinedpressure of the spring 106 and the propellant gas pressure active on thefiring pin sealing flange 102 after firing of the round is effective tourge the flange into a sealing contact with the rear end of itscontaining chamher 104, about the bore 108, thus to seal this boreagainst propellant gas leakage. Thus, the sealing flange 102 forms partof the obturator means 42 of the illustrated breech mechanism.

It is evident at this point, that the obturator means 42 comprisepressure responsive sealing elements or flanges which are exposed to thepressure of the propellant gas generated within the cylinder chamber 24during firing of a caseless round 12 in the chamber, with the cylinder18 in its firing position, and which are urged or deflected by such gaspressure into sealing contact with the corresponding cylinder sealingsurfaces. All of the leakage interfaces 32, 34, 36, and 38 of the breechmechanism are thus effectively sealed against propellant gas leakage toprovide maximum gas pressure for driving the projectile 30 through thegun bore 28.

As noted earlier, another important aspect of the invention is concernedwith the construction of the caseless round 12. According to thisaspect, the invention provides a caseless round having a shaped,caseless propellant charge 110 of the same triangular round shape intransverse cross-section as the cylinder firing chamber 24. Accordingly,when the round 12 is positioned in the chamber, its caseless propellantcharge 110 completely fills the chamber and the outer cylindricallycurved side of the charge is flush with the circumference of thecylinder 18. The triangular shape of the present caseless round offersthe same advantages as those discussed in the aforementioned patentswhich disclose open chamber breech mechanisms for firing casedammunition. Accordingly, there is no need to repeat in detail thevarious advantages of the triangular shape. Suffice it to say, theseadvantages include those of automatic orientation of the charge in thefiring chamber, elimination of jamming, compact storage, and others. Thetriangular shape of the present caseless round has one additionalimportant benefit in that it permits maximum propellant weight for agiven overall propellant charge size. This shaped caseless propellantcharge may be molded from any conventional caseless propellant materialby any of the known molding techniques. As noted earlier, the presentbreech mechanism is susceptible of various non-weapon applications. Inat least some of these latter applications, wherein the sole requirementis the generation of a high pressure gas, the propellant charge may besolid in cross-section.

Another important feature of the illustrated caseless round 12 residesin the fact that the projectile 30 is effectively encapsulated entirelywithin the shaped, caseless charge 110, as shown in the drawing. Thisparticular caseless round configuration presents several advantages.First the round has minimum overall size which results in a volumetricstorage space saving on the order of 30% for the same charge-mass ratio,compared to a typical conventional caseless round to be describedpresently in connection with the modified breech mechanism of FIGS. and6. A second and highly important advantage of the present caseless roundconfiguration resides in the fact that the projectile 30, beingencapsulated as it is within the propellant charge 110, is not prone toseparation from the charge during handling or infeed movement to thebreech mechanism. As a consequence, the present caseless round iscapable of much rougher handling and use in high speed automaticweapons. Moreover, as will appear from the ensuing description, thepresent caseless round configuration simplfies construction and sealingof the open chamber breech mechanism. Referring to FIGS. 1 and 2, itwill be observed that the projectile 30 of the caseless round 12 isencapsulated within the shaped propellant charge 110 in such a way thatthe longitudinal axis of the projectile coincides with the longitudinalaxis of the charge. Accordingly, when the round is positioned within theopen chamber 24 of the cylinder 18, and the latter is rotated to itsfiring position, the projectile is coaxially aligned with the gun bore28 and cylinder bore 60. The propellant gas generated by firing of thepropellant charge 110 is thus effective to drive the projectile forwardat high velocity through the gun bore. It is evident, of course, thatbecause of the complementary, general equilateral triangular shapes ofthe illustrated caseless round 12 and cylinder chamber 24, the round maybe placed in the chamber with any one of its sides exposed. However, thefiring chamber and caseless round may have the somewhat modifiedgenerally triangular round shapes disclosed in Patent No. 2,847,784.

In connection with the possibility of jamming of the ca eless round 12between the breech frame 14 and the cylinder 18 during rotation of thelatter to its firing position, it is significant to recall that theexposed surface of the round, when positioned in the cylinder chamber24, is substantially flush with the circumference of the cylinder. As aconsequence, the round can rotate without interference past thelongitudinal obturator sealing flange 78 which is located adjacent thebreech frame infeed opening 26 during rotation of the cylinder 18 to itsfiring position. This elimination of interference between the sealingflange and the round, of course, is aided by the fact the flange is noturged to sealing position by propellant gas pressure during rotation ofthe cylinder to its firing position. Moreover, even though the round isnot properly oriented in the cylinder chamber 24, engagement of thesealing flange 78 with the round, during rotation of the cylinder to itsfiring position, will cam the round to its proper position in thechamber. Additional insurance against jamming, as well as reduction ofthe frictional resistance to rotation of the cylinder 18 to and from itsfiring position is achieved by the offset relation of the rotation axis22 and the central axis 66 of the cylinder. In this regard, attention isdirected to FIG. 2, wherein it will be observed that these axes areoffset or displaced in such a way that the circumference of the cylinderrecedes from the obturator sealing flanges 78, 80 and 82 during rotationof the cylinder from its firing position to its infeed position andapproaches the sealing flanges during rotation of the cylinder from itsinfeed position to its firing position. According to the presentinvention, the spacing of the rotation axis from the central axis of thecylinder is made such that the circumference of the cylinder recedesfrom contact with the obturator sealing flanges during rotation of thecylinder to its infeed position and returns to contact with the sealingflanges just prior to arrival of the cylinder in its firing position. Inthis way, sliding friction between the cylinder 18 and the breech frame14 during rotation of the cylinder to and from its firing position isminimized and a slight clearance is provided between the left handobturator sealing flange 78 in FIG. 2 and the exposed surface of thecaseless round 12 in the cylinder chamber 24 during rotation of theround past the flange to firing position. The possibility of jamming ofthe round against or damage to the round by the flange is thus virtuallyeliminated.

Briefly summarizing the operation of the breech mechanism 10, thecylinder 18 is rotated to its infeed position and a caseless round 12 islaterally positioned in the cylinder chamber 24. The cylinder is thenrotated to its firing position and the propellant charge of the round isfired by actuation of the firing mechanism 40. The resulting propellantgas pressure drives the projectile 30 forwardly through the gun bore 28.The propellant gas pressure also urges or deflects the several pressureresponsive sealing flanges of the obturator means 42 to sealingposition, thus to effectively seal the breech mechanism againstpropellant gas leakage through the leakage interfaces 32, 34, 36, and 38of the mechanism.

At this point, attention is directed to the fact that while the cylinderof the breech mechanism 10, as well as the other breech mechanismshereinafter described, is supported on the breech frame for oscillatorymovement between its infeed and firing positions, the cylinder may besupported for rotation in one direction to its loading and firingpositions in alternate sequence. Moreover, it is evident that while theillustrated breech mechanisms have a single firing chamber, thecylinders of the mechanism may be provided with a number of chamberslike the breech mechanisms disclosed in the aforementioned patents. Inaddition, while the disclosed breech mechanisms are designed for manuallodging of each caseless round into the cylinder firing chamber, apresent breech mechanism may employ any suitable ammunition infeedsystem such as those disclosed in the patents.

The modified, sealed, open chamber breech mechanism 200 of the inventionwhich has been illustrated in fragmentary fashion in FIG. 4 is identicalto the breech mechanism 10, just described, except that the breech frame202 of the breech mechanism 200 has a tapered rearwardly opening orifice204 which communicates with the firing chamber 206 in the breechcylinder 208 through a passage 210 in the breech obturator 212 when thecylinder occupies its illustrated firing position. The modified breechmechanism 200 is otherwise identical to the breech mechanism 10.

During firing of a caseless round 12 in the firing chamber 206 of thebreech mechanism 200, with the cylinder in its firing position of FIG.4, a portion of the propellant gas expands rearwardly at high velocitythorugh the orifice 204 to create a forward counter-recoil force on thebreech mechanism in opposition to the rearward recoil force resultingfrom forward expansion of the propellant gas to drive the projectile 30forwardly through the gun bore. According to the present invention, theorifice 204 is so shaped and sized that the recoil and counter-recoilforces balance one another, whereby the breech mechanism of FIG. 4 has arecoilless firing action. It will be understood, of course, that thebreech mechanism 200, like the breech mechanism 10, embodies obturatormeans including the upper obturator 212 for sealing the several leakageinterfaces of the mechanism during firing.

Reference is now made to FIGS. 5 and 6 which illustrate a furthermodified sealed, open chamber breech mechanism 300 according to theinvention, for firing a conventional caseless ammunition round 302. Thisconventional caseless round has a rear, shaped propellant charge 304 ofsolid circular cross-section and a forward projectile 306 secured to andextending forwardly from the front end of the shaped charge.

The modified breech mechanism 300 is essentially identical, in mostrespects, to the earlier described breech mechanism 10 of the invention.Accordingly, it is unnecessary to describe the breech mechanism 300 incomplete detail. Suffice it to say, that the breech mechanism 300differs in only two respects from the breech mechanism 10. One of thesedifferences involves the shape of the breech cylinder 308 and its firingchamber 310, and the other difference involves the construction of theupper breech obturator 312. With regard to the shape of the breechcylinder 308, it will be observed, particularly in FIG. 6, that the sideof the cylinder, containing the firing chamber 310, is recessed in theregion between the ends of the chamber to provide the cylinder with agenerally planar chord face 314 parallel to the rotation axis 316 of thecylinder. The leading longitudinal edge of this face relative to thedirection of rotation of the cylinder 308 toward its firing position ofFIGS. 5 and 6, i.e., the righthand edge of the face in FIG. 6, extendsoutwardly to and intersects the circumference of the cylinder. Theopposite, trailing longitudinal edge of the cylinder face 314 terminatesat and joins a shoulder face 318 which extends outwardly from the chordface to the circumference of the cylinder, approximately in a radialplane of the cylinder. The firing chamber 310 of the cylinder 308 isformed in the cylinder chord face 314. It will be observed that thisfiring chamber is generally semicircular in crosssection. The rearportion of the chamber is designed to receive and has substantially thesame radial and axial dimensions as the rear propellant charge 304 ofthe caseless round 302. The front portion of the chamber is designed toreceive and has substantially the same radial and axial dimensions asthe front projectile 306 of the round. The firing chamber 310 is thusconditioned to receive the round 302 in the manner illustrated best inFIG. 5.

The modified upper breech obturator 312 of the breech mechanism 300 issimilar to the obturator 68 of the breech mechanism 10 in that theobturator 312 comprises a generally fiat rectangular bar which is shapedto define an interior cavity 320 within the obturator having an openside which faces the cylinder 308 and is bounded by inwardly directed,longitudinal sealing flanges 322, a front lateral sealing flange 324,and a rear lateral sealing flange 326. These sealing flanges areresiliently deflect-ible toward and into sealing contact withcorresponding sealing surfaces on the cylinder 308, about the cylinderrecess containing the firing chamber 310. Thus, the longitudinal sealingflanges 322 are engageable with longitudinal sealing surfaces 328furnished by the circumferential portions of the cylinder 308 whichbound the longitudinal sides of the cylinder recess. The front lateralsealing flange 324 is engageable with a front lateral sealing surface330 on the cylinder furnished by a conically tapered circumferentialportion of the cylinder founding the front end of the cylinder recess.Finally, the rear lateral sealing flange 326 is engageable with asealing surface 332 on the cylinder furnished by a rear cylindricalcurved circumferential portion of the cylinder bounding the rear end ofthe cylinder recess. As in the earlier breech mechanism 10, of theinvention, the propellant gas generated by firing of a caseless round302 in the firing chamber 310; with the cylinder 308 in its firingposition, enters the obturator cavity 320 and acts on the inner pressurefaces of the Sealing flanges 322, 324, 326 to urge these flanges intosealing contact with the respective cylinder sealing surfaces 328, 330and 332, thereby to seal the breech mechanism against propellant gasleakage through the open side of the cylinder recess.

The obturator 312 in the modified breech mechanism 300 is also equippedwith a hinged projectile obturator and guide 334 in the form of agenerally rectangular plate or flapper which is pivotly mounted by ahinge pin 336 for swinging on an axis parallel to and laterallydisplaced from the central axis of the firing chamber 10. The dimensionof the plate 334, lengthwise of the cylinder 308, approximates thelength of the forward, projectile receiving portion of the firingchamber 310. In the region adjacent the obturator plate, the obturatorcavity 320 is enlarged, as shown, to accommodate swinging or hinging ofthe plate in the manner hereinafter described. Acting between the plateand the wall of the cavity is a compression spring 338 for urging theplate toward the cylinder 308. The side of the plate facing the cylinderhas a generally plannar surface 340 which is disposed for flat surfacecontact with the planar chord face 314 on the cylinder 308 when thelatter occupies its firing position of FIGS. 5 and 6. Joining andextending from the plate surface 340 to the hinge pin 336 of the plate,at an angle relative to the surface, is an inclined camming surface 342.Formed in the plate surface 340 is a semi-cylindrical groove 344 whichis disposed to receive the forward projectile 306 of the caseless round302 when the plate occupies its position in FIG. 6, hereinafter referredto as its sealing position. The radius of the plate groove 344 issubstantially the same as the external radius of the projectile.

When the breech cylinder 308 is rotated to its firing position of FIGS.5 and 6, with a caseless round 302 in the firing chamber 310, theobturator plate 334 seats against the cylinder to seal the open side ofthe forward, projectile receiving end of the chamber. The plate alsocooperates with the cylinder to guide the projectile 306 in its initialforward movement from the firing chamber, through the cylinder bore 346,into the gun bore 348 following firing of the propellant charge 304 inthe chamber.

Except for the structure described above, the breech mechanism 300 isidentical to the earlier breech mechanism 10 of the invention.Accordingly, no further structural description of the mechanism 300 isnecessary.

During operation of the breech mechanism 300, the breech cylinder 308 isrotated in a counterclockwise direction in FIG. 6 to its infeedposition, wherein the open firing chamber 310 in the cylinder is exposedthrough the ammunition infeed opening 350 in the breech frame 352 toreceive a caseless round 302 through the opening. During this rotationof cylinder to its infeed position, the right hand longitudinal cylinderedge of FIG. 6, defined by the intersection of the cylinder chord face314 with circumference of the cylinder, engages the beveled camingsurface 342 on the projectile obturator plate 334 and rotates orretracts the plate upwardly in FIG. 6, against the action of the platespring 38, to accommodate rotation of the cylinder from its firingposition. The plate eventually rides onto the circumferential surface ofthe cylinder as latter approached its infeed position. During rotationof the cylinder 308 back to its firing position, with the caseless round302 in the firing chamber 310, the plate 334 is retained in itsretracted position until the cylinder is just short of its firingposition. The plate is then released for return to its sealing positionof FIG. 6, upon final rotation of the cylinder to its firing position.As noted earlier, the obturator plate 334, when in this sealingposition, effectively seals the open side of the forward projectilereceiving end of the firing chamber 10, about the projectile 306therein, and cooperates with the cylinder to guide the projectile fromthe firing chamber into the gun bore 348 under the action of thepropellant gases generated during subsequent firing of the propellantcharge 304.

In connection with the sealing function of the obturator plate 334, itwill be observed that propellant gas pressure acting on the uppersurface of the plate in FIG. 6 aids the obturator spring 338 inretaining the plate in sealing contact with the chord face 314 of thecylinder 308.

Turning now to FIGS. 7-9, there is illustrated a modified'sealed, openchamber breech mechanism 400 according to the invention which isidentical except for the obturator means, to the earlier describedbreech mechanism 10. Accordingly, there .is no need to describe thebreech mechanism 400 in complete detail. Suffice it to say that thisbreech mechanism comprises a hollow breech frame 402 containing acylinder recess 404 in which is rotatably supported a breech cylinder406 for turning on an axis 408. The cylinder has an overall geometrywhich is identical to that of the breech cylinder 18 of the breechmechanism 10. The breech mechanism 400 differs from the earlier breechmechanism only in that the upper breech obturator 68 of the lattermechanism is eliminated in the breech mechanism 400 and the cylinderrecess 404 is bounded, along its normally upper side by a rear surface410 of cylindrical curvature which is generated about the central axis412 of the cylinder 406 and a forward surface 414 having a conicalcurvature also generated about the axis 412. The curvature of the framesurface 410 conforms to the cylindrical curvature of cylinder 406, whilethe curvature of the frame surface 414 conforms to the curvature of theforward conically tapered surface of the cylinder. The rotation axis 408and central axis 412 of the cylinder 406 are laterally offset, inessentially the same manner as the corresponding axes of the earlierbreech mechanism, and in such a way that when the cylinder occupies itsfiring position, the breech frame surfaces 410, 414 seat flush againsttheir corresponding cylinder surfaces, as illustrated. When the cylinderis rotated from its firing position to its infeed position, the cylindersurfaces recede from the frame surfaces 410, 414 to minimize thefrictional drag imposed on the cylinder by the breech frame, thus tofacilitate rotation of the cylinder to and from its firing position.

The major difference between the breech mechanism 400 underconsideration and the earlier breech mechanism of the invention residesin the modified obturator means 416 embodied in the mechanism 400. Thesemodified obturator means include a pair of longitudinal sealing elements418 and a pair of lateral sealing elements 420 for sealing the leakageinterfaces between the breech frame 402 and cylinder 406, about the openside of cylinder firing chamber 422, and a front seal ring 424 forsealing the leakage interface about the communicating ends of theforward cylinder bore 426 and the gun bore 428 in the gun barrel 430.The longitudinal and lateral sealing elements 418, 420 are containedwithin corresponding sealing grooves 432 which are formed in thecircumference of the breech cylinder 406, along the 1ongitudinal sidesand across the front and rear ends, respectively, of the firing chamber422. The seal ring 424 is contained within an annular sealing groove 433in the front end of the cylinder 406, about the cylinder bore 426. Itwill be observed that the firing chamber 422 and the longitudinal andlateral sealing grooves 432 define therebetween relatively thinintervening Wall sections 434 which extend radially out to thecircumference of the cylinder. The forward cylinder bore 426 and theannular seating groove 434 define therebetween a relatively thin annularwall section 436 which extends axially to the front end of the cylinder406.

The breech mechanism 400 under discussion is designed to fire a caselessround 12 of the kind described earlier in connection with the breechmechanism 10. During firing of this round in the firing chamber 422,with the breech cylinder 406 in its firing position, the propellant gaspressure acts on the several cylinder wall sections 434, 436 indirections to urge these wall sections toward their adjacent sealinggrooves 432, 434, as the case may be. According to the presentinvention, these wall sections have a thickness such that the propellantgas pressure is effective to resiliently deflect or urge the sectionstoward their adjacent sealing grooves, thereby to laterally compress thesealing elements 418, 420, 424, and 426 in the grooves. Further thesesealing elements are constructed of a material, such as asbestos, which,when compressed in a lateral direction of the sealing grooves bydeflection of the cylinder wall sections 434, 436, is distended from thesealing grooves into sealing contact with the confronting breech framesurfaces. In this regard, it will be observed that the longitudinal andlateral sealing elements 418, 420 are arranged for distension bypropellant gas pressure from their respective sealing grooves 434 intosealing contact with the breech frame surfaces 410 and 414, as the casemay be. The seal ring 424 is arranged for axial distension by propellantgas pressure into sealing contact with rear annular face of the gunbarrel 430. These breech frame and gun. barrel surfaces thus function asbreech frame sealing surfaces.

The open chamber breech mechanism 400 is otherwise identical to theearlier described breech mechanism 10 of the invention. Moreover, theoperation of the breech mechanism 400 is essentially identical to thatof the breech mechanism 10. Accordingly, there is no need for a furtherdetailed structural or functional description of the mechanism 400, withthe breech cylinder 406 in its firing position of FIGS. 7 and 8, thepropellent gas pressure generated within the chamber is effective todeflect the cylinder wall sections 434, 436 into compressive contactwith the adjacent sealing elements 418, 420, 424, and 426 and therebydistend the elements into sealing contact with their respective sealingsurfaces on the breech frame 402. Thus, the modified obturator means 416of the breech mechanism 400 are effective to seal the'leakage interfacesof the mechanism against propellant gas leakage and thereby providemaximum propellant gas pressure for driving the projectile 30 of thecaseless round 12 forwardly through the gun bore 428. If desired, theintegral cylinder wall sections 434 in the breech mechanism 400 may bereplaced by hinged wall sections of the kind illustrated at 434a in FIG.10.

It is now evident that the various open chamber breech mechanism sealingtechniques disclosed herein possess all of the advantages heretoforediscussed. Another distinctive advantage of these techniques resides inthe fact that the sealing elements of the breech mechanisms areelastically deformed or deflected to their sealing positions bypropellant gas pressure. Because of the elastic memory of the sealingelements, the latter retract from their sealing positions when thepropellant gas pressure is removed at the end of the firing cycle.

This elastic return of the sealing elements to their initial positionsafter firing further reduces the frictional drag on the cylinders of thebreech mechanisms during 13 rotation of the cylinders to and from theirfiring positions.

At this point, attention is again directed to the fact that while theinvention has been disclosed in connection with its application to openchamber breech type weapons or guns, the sealing techniques proposed bythe invention may be utilized to advantage in open chamber breechmechanisms for other purposes. These latter applications of theinvention will not be explained in detail. Suffice it to say that someof the additional applications of the present open chamber sealingtechniques are stud drivers, nail drivers, stake drivers, slaughterguns, cable splicers, oil well perforators, open chamber solid or liquidpropellant engines for space ship attitude control, and, in general, apropellant gas source for any purpose. The rounds employed in some ofthese latter applications may contain projectiles and in otherapplications may comprise only a propellant.

The embodiments of the invention in which an exclusive property orprivilege is claimed are defined as follows:

1. An open chamber breech mechanism for firing a round of caselessammunition comprising:

a hollow breech frame member;

a carrier member supported in said frame member for rotation on an axisand having a firing chamber opening laterally through the circumferenceof said carrier member;

said carrier member being rotatable in said frame member to locate saidfiring chamber in an ammunition infeed position, wherein the open sideof said firing chamber registers with an ammunition infeed opening insaid frame member for receiving said round through said opening, and afiring position, wherein said frame member closes the open side of sadifiring chamber to condition said breech mechanism for firing said roundin said firing chamber to generate a high pressure propellant gas insaid firing chamber;

means defining a bore which communicates with said firing chamber whensaid firing chamber occupies said firing position and through which saidpropellant gas exhausts from said firing chamber;

said members defining therebetween leakage interfaces which communicatewith said firing chamber when said firing chamber occupies said firingposition; and

coating obturator means on said members for sealing said interfacesagainst propellant gas leakage during firing of said round in saidfiring chamber with said firing chamber in said firing position.

2. An open chamber breech mechanism according to claim 1, wherein saidobturator means comprise pressure responsive sealing means which areexposed to and urged to sealing position by said propellant gaspressure.

3. An open chamber breech mechanism according to claim 1, wherein saidobturator means comprise circumferential sealing surface means on saidcarrier member about the open side of said firing chamber, and pressureresponsive sealing means on said frame member which are exposed to andurged into sealing relation with said sealing surface means by saidpropellant gas pressure.

4. An open chamber breech mechanism according to claim 1, wherein saidobturator means comprise circumferential sealing surface means on saidframe member which span the open said of said firing chamber when saidfiring chamber occupies said firing position, and pressure responsivesealing means on said carrier member which are exposed to and urged intosealing relation with said sealing surface means by said propellant gaspressure.

5. An open chamber breech mechanism for firing a round of caselessammunition comprising:

a hollow breech frame member;

a carrier member supported in said frame member for rotation on an axisand having a firing chamber opening laterally through the circumferenceof said carrier member;

said carrier member being rotatable to locate said firing chamber in anammunition infeed position, wherein the open side of said firing chamberregisters with an ammunition infeed opening in said frame member forreceiving said round through said opening, and a firing position,wherein said frame member closes the open side of said firing chamber tocondition said breech mechanism for firing said round in said firingchamber to generate a high pressure propellant gas in said firingchamber;

means defining a bore which communicates with said firing chamber whensaid firing chamber occupies said firing position and through which saidpropellant gas exhausts from said firing chamber;

said members defining therebetween leakage interfaces which communicatewith said firing chamber when said firing chamber occupies said firingposition; and

obturator means comprising sealing surface means on one of said membersbounding each of said interfaces, and elastically deformable sealingmeans on the other members which are exposed to and elastically deformedinto sealing relation with said sealing surface means by said propellantgas pressure.

6. An opening chamber breech mechanism according to claim 5, whereinsaid sealing means comprise elastic sealing flanges which areelastically deflected into sealing relation with the respective sealingsurface means by said propellant gas pressure.

7. An open chamber breech mechanism according to claim 5, wherein saidsealing means comprise resiliently compressible sealing elements whichare compressed in one direction by said propellant gas pressure andthereby distended in another direction into sealing relation with therespective sealing surface means.

8. An open chamber breech mechanism according to claim 7, wherein saidobturator means further comprise pressure wall means disposed in seatingcontact with said compressible sealing elements, respectfully, andexposed to the interior of said firing chamber for exerting acompressive force on the adjacent sealing elements in response to saidpropellant gas pressure on said wall means.

9. An open chamber breech mechanism according to claim 8, wherein saidwall means are elastically deflected into compressive contact with theadjacent sealing elements under the force of said propellant gaspressure on said wall means.

10. An open chamber breech mechanism according to claim 8, wherein saidwall means are pivotally mounted for rocking movement into compressivecontact with the respective sealing elements under the force of saidpropellant gas pressure on said wall means.

11. An open chamber breech mechanism for firing a round of caselessammunition comprising:

a hollow frame;

a cylinder supported in said frame for rotation on the cylinder axis andhaving a firing chamber opening laterally through the cylindercircumference;

said cylinder being rotatable to locate said firing chamber in anammunition infeed position, wherein the open side of said firing chamberregisters with an ammunition infeed opening in said frame and receivingsaid round through said opening, and a firing position, wherein saidframe closes the open side of said firing chamber to condition saidbreech mechanism for firing said round in said firing chamber togenerate a high pressure propellant gas in said firing chamber;

means defining a bore which communicates with said firing chamber whensaid firing chamber occupies said firing position and through which saidpropellant gas exhausts from said firing chamber;

said frame and cylinder defining therebetween leakage interfaces whichcommunicate with said firing chamber when said firing chamber occupiessaid firing position; and

obturator means for sealing said interfaces against propellant gasleakage during firing of said round in said firing chamber with saidfiring chamber in said firing position including circumferential sealingsurfaces on said cylinder about the open side of said firing chamber,and an obturator member on said frame including elastically defiectablesealing elements having sealing surfaces disposed in confrontingrelation to and conforming to the curvature of said cylinder sealingsurfaces, respectively, and pressure faces on which said propellant gaspressure acts to deflect said sealing elements into sealing relationwith the respective cylinder sealing surfaces.

12. An open chamber breech mechanism according to claim 11, wherein saidobturator member contains a cavity having an open side disposed toregister with the open side of said firing chamber when said firingchamber occupies said firing position, and said obturator sealingelements comprise inwardly directed elastically deflectable sealingflanges on said obturator member about the open side of said cavity andhaving inner surfaces exposed to said cavity and forming said pressurefaces.

13. An open chamber breech mechanism for firing a round of caselessammunition comprising:

a hollow breech frame;

a cylinder supported in said frame for rotation on the cylinder axis andhaving a firing chamber opening laterally through the cylindercircumference;

said cylinder being rotatable to locate said firing chamber in anammunition infeed position, wherein the open side of said firing chamberregisters with an ammunition infeed opening in said frame for receivingsaid round through said opening, and a firing position, wherein saidframe closes the open side of said firing chamber to condition saidbreech mechanism for firing said round on said firing chamber togenerate a high pressure propellant gas in said firing chamber;

means defining a bore which communicates with said firing chamber whensaid firing chamber occupies said firing position and through which saidpropellant gas exhausts from said firing chamber;

said breech frame having a circumferential sealing surface disposed insliding contact with the circumference of said cylinder;

said sealing surface and cylinder circumference defining therebetween aleakage interface communicating with said firing chamber when saidfiring chamber occupies said firing position; and

obturator means for sealing said interface against propellant gasleakage during firing of said round in said firing chamber with saidfiring position including resiliently compressible sealing elementsdisposed in grooves in the circumference of said cylinder about the openside of said firing chamber, and pressure responsive wall membersbetween and bounding said grooves and firing chamber for transmittingsaid propellant gas pressure to said sealing elements for compressingsaid elements laterally and thereby distending said elements radially ofsaid cylinder into sealing relation with said frame sealing surface.

14. An open chamber breech mechanism according to claim 1, wherein:

said obturator means comprise cylindrically curved sealing surface meanson one of said members generated about an axis of curvature, and sealingmeans on the other member engageable with said sealing surface meansabout the open side of said firing chamber when said firing chamberoccupies said firing position; and

said axes are disposed in spaced parallel relation in such manner thatsaid sealing means and sealing surface means approach one another duringrotation of said firing chamber to said firing position and recede fromone another during rotation of said firing chamber from said firingposition.

15. An open chamber breech mechanism according to claim 14, wherein saidsealing means comprise elastically deformable sealing elements which areexposed to and elastically deformed into sealing relation with saidsealing surface by propellant gas pressure.

16. An open chamber breech mechanism for firing a round of caselessammunition containing a projectile comprising:

a hollow breech frame member;

a carrier member supported in said frame member for rotation on an axisand having a firing chamber opening laterally through the circumferenceof said carrier member;

said carrier member being rotatable to locate said firing chamber in anammunition infeed position, wherein the open side of said firing chamberregisters with an ammunition infeed opening in said frame member forreceiving said round through said opening and a firing position, whereinsaid frame member closes the open side of said firing chamber tocondition said breech mechanism for firing said round in said firingchamber to generate a high pressure propellant gas in said firingchamber;

a barrel on said frame member having a bore opening at one end to theinterior of said frame member and disposed in spaced parallel relationto said rotation axis in such manner that said firing chamber iscoaxially aligned with and opens forwardly to said bore when said firingchamber occupies said firing positions;

said frame member and carrier member defining therebetween a firstpropellant gas leakage interface about said bore, and said frame memberand the circumference of said carrier member defining therebetween asecond propellant gas leakage interface about the open side of saidfiring chamber when said firing chamber occupies said firing position;and

first coacting obturator means on said members for sealing said firstleakage interface against propellant gas leakage and second coactingobturator means on said member for sealing said second leakage interfaceagainst propellant gas leakage during firing of said round in saidfiring chamber with said firing chamber in firing position.

17. An open chamber breech mechanism according to claim 16, wherein eachof said obturator means comprise pressure responsive sealing means whichare exposed to and urged to sealing position by said propellant gaspressure.

18. An open chamber breech mechanism according to claim 16, wherein saidfirst obturator means comprise confronting surfaces on said membersdisposed in surrounding relation to the communicating ends of said boreand firing chamber, one of said surfaces comprising a sealing surface,an annular sealing groove entering the other surface in coaxial relationto the communicating ends of said bore and firing chamber and openingaxially toward said sealing surface, an elastic radially compressibleaxially distendable seal ring positioned in said groove, and the innerannular wall of said groove being exposed to and radially deflectibleinto compressible contact with said seal ring by said propellant gaspressure to compress said seal ring radially and thereby distend saidseal ring axially into sealing relation with said sealing surface.

19. An open chamber breech mechanism according to claim 18, wherein:

said firing chamber has an end wall containing a bore which is coaxiallyaligned with said first-mentioned bore when said firing chamber occupiessaid firing position; and

said sealing surface is on said frame member and said groove is in saidcarrier member and disposed in coaxial surrounding relation to said endWall bore.

20. An open chamber breech mechanism according to claim 16, wherein:

said firing chamber has an end wall containing a bore which is coaxiallyaligned with said first-mentioned 1 7 bore when said firing chamberoccupies said firing position; and

said first obturator means comprise confronting surfaces on said membersdisposed in surrounding relation to the communicating ends of saidbores, the confronting surface on one of said members being a sealingsurface, the bore in the other member having an internal circumferentialgroove defining with the confronting surface on the latter member anintervening annular, axially defiectible sealing flange which is urgedinto sealing relation with said sealing surface about said bores by saidpropellant gas pressure.

21. An open chamber breech mechanism according to claim 20, wherein saidsealing surface is on said member and said sealing flange is on saidcarrier member.

22. An open chamber breech mechanism according to claim 16, wherein:

said carrier member comprises a cylinder;

said first obturator means comprise a sealing surface on one of saidmembers disposed in surrounding relation to the communicating ends ofsaid bore and firing chamber, and an annular elastically deformablepressure responsive sealing element on the other member which isdisposed in coaxially surrounding relation to the communicating ends ofsaid bore and firing chamber when said firing chamber occupies saidfiring position and is urged into sealing relation with said sealingsurface by said propellant gas pressure; and

said second obturator means comprise circumferential sealing surfacemeans on one of said members, and elastically deformable sealingelements on the other member which are disposed in surrounding relationto said firing chamber and in confronting relation to said lattersealing surface means when said firing chamber occupies said firingposition and are urged into sealing relation with said latter sealingsurface means by said propellant gas pressure.

23. An open chamber breech mechanism according to claim 16, wherein:

said round comprises an uncased propellant charge and a projectilesecured to and extending forwardly from the front end of said charge;

said carrier member comprises a cylinder;

said firing chamber has a rear portion shaped to complement and receivesaid propellant charge and a forward semi-cylindrical portion forreceiving said projectile; and

said second obturator means comprise an obturator member on said framemember including elastically defiectible sealing flanges which surroundthe open side of said firing chamber and have sealing surfaces disposedin confronting relation to the circumference of said cylinder about saidopen side when said firing chamber occupies said firing position, saidsealing surfaces having the same curvature as the circumference of saidcylinder and said flanges having pressure faces exposed to thepropellant gas pressure on which said pressure acts to urge said flangesinto sealing relation with said cylinder circumference about the openside of said firing chamber during firing of said round in said chamber,and an obturator plate pivotally mounted on said obturator member forswinging between an extended position, wherein one face of said plateseats against said cylinder at opposite sides of said semi-cylindricalchamber portion, and a retracted position, wherein said plates clearssaid cylinder for rotation of said firing chamber from said firingposition, a spring acting between said plate and obturator member forurging said plate to said extended position, and said face of said platehaving a semi-cylindrical groove which registers with saidsemi-cylindrical chamber portion when said plate occupies said extendedposition to define an obturating guide bore for guiding said projectilein its forward movement from said firing chamber under the force of saidpropellant gas pressure.

24. An open chamber breech mechanism according to claim 1, including:

a firing mechanism on one of said members for firing said ammunitionround in said firing chamber when said firing chamber occupies saidfiring position; and

obturator means for sealing said firing mechanism against propellant gasleakage.

25. An open chamber breech mechanism according to claim 11, wherein saidbored defining means comprises a barrel which extends forwardly of saidframe member and is coaxially aligned with said firing chamber in firingposition, and breech frame has a rearwardly opening venturicommunicating with said firing chamber when in firing position throughwhich a portion of the propellant gas generated during firing exits athigh velocity to produce a counter-recoil force on said mechanism.

References Cited UNITED STATES PATENTS 9/1885 Tyler. 9/1961 Thierry t8926 FOREIGN PATENTS 1914 Great Britain. 1903 Sweden.

BENJAMIN A. BORCHELT, Primary Examiner.

STEPHEN C. BENTLEY, Assistant Examiner.

US. Cl. X.R. 42-395; 89-155 Patent No. 3 ,446 ,113 May 27 1969 DavidDardick It is certified that error appears i patent and that saidLetters Patent are hereby 0 shown below:

n the above identified orrected as second occurrence, insert line 49after "firing" line 31, "bored" should Column 15 C olumn 18,

chamber in said firing read bore Signed and sea1ed this 23rd day of June1970.

(SEAL) Attest:

Edward M. Fletcher, Jr.

Commissioner of Patents Attesting Officer WILLIAM E. SCHUYLER, JR.

